The present invention relates to a rotor, especially a rotor for a steam turbine with disks thermally shrink-fitted on the rotor shaft and with fixing keys between each disk and the shaft.
In prior art arrangements, a rotor of a steam turbine has been made by an integral formation of disks and a shaft. With a large size of steam turbine corresponding to a high capacity thereof, an integral manufacture is difficult because of the practical production problems, so that rotors for high capacity turbines are, as a practical matter required to be manufactured with individual rotor disks thermally shrink-fitted on a rotor shaft. Thermal shrinking of rotor disks onto a rotor shaft is made with a sufficient shrink tolerance between the disks and the shaft so as to avoid slippage between the contacting surfaces thereof and to transfer a sufficient torque.
As a further aid in avoiding slippage between the rotor disks and rotor shaft, it has been contemplated to dispose keys between the disks and rotor shaft.
An object of the invention is to reduce the thermal deflection of a rotor shaft with a key for a double flow type of steam turbine.
Another object of the invention is to provide a rotor for a double flow type of steam turbine in which a thermal deflection of a rotor shaft is made small in the area where the first stages are arranged on a shaft adjacent to each other.
Another object of the invention is to provide a thermally shrink-fitted rotor for a steam turbine, employing a new key arrangement to make thermal deflection of a rotor shaft small.
Another object of the invention is to offset thermal distortion on a rotor shaft caused by the key.
In a low pressure turbine a phenomenon in which the vibration of a rotor was excessive at a critical speed had occurred as a phenomenon particular to a thermally shrink-fitted rotor when a turbine speed was gradually decreased from the rated speed upon a load disconnection. Further, the vibration also increased when a load was connected in the rated speed. The cause of the phenomenon was investigated, and it was discovered by the inventors that the vibration had occurred due to a thermal deflection of the shaft. The thermal deflection particular to the thermally shrink-fitted rotor was caused by an unbalanced heat conductivity particular to the shaft flowing from a disk to the shaft. Especially in a double flow type of steam turbine the imbalance of the heat conductivity was large in the first stages in the region of the highest temperature in the stages. The heat transferred to blades from a steam turbine is conducted to the shaft through the disk. In the thermally shrink-fitted rotor there is provided a key groove and a key closely disposed in the groove between the disk and the shaft. This key arrangement makes the heat conductivity decrease around the key. The decreasing of the heat conductivity on a part of the shaft causes the thermal deflection on the shaft due to the temperature difference to the other portion. This was ascertained by experiments and a calculation with respect to the thermal deflection by using a computer. The inventors discovered the reason for the thermal deflection of a rotor shaft was distortion of the temperature distribution of the shaft caused by key means and provided thermal balancing means for counteracting such thermal distortions of the shaft.